OTTAWA - NDP leadership hopeful Brian Topp is advancing a new reason to abolish Canada's unelected Senate: its potential to paralyze a national New Democrat government.

Should he become prime minister, Topp says he'd quickly introduce a constitutional amendment to do away with the "antiquated" upper house, which is made up entirely of Conservative and Liberal appointees.

He says he'd pursue abolition as "an immediate and urgent priority" if senators were to provoke a constitutional crisis by blocking the NDP government's budget or other important legislation.

He'd pursue the matter "more deliberately" with the provinces, which would need to approve an abolition amendment, as long as senators returned to their "traditional role" as subordinate to the elected House of Commons.

Topp's Senate proposal is part of a three-pronged approach he says would help restore responsible government in Canada.

He's also proposing to limit the prime minister's power to prorogue Parliament and introduce a mixed proportional electoral system, to end the distortions that result from the current first-past-the-post system of electing MPs.

On the latter, Topps says the NDP should ask for a mandate in the next election to create a new tier of MPs, who would be elected based on their parties' proportional share of the national vote. They would be in addition to MPs elected by the traditional method, which has resulted in parties winning a majority of seats with less than 40 per cent of the vote.

Various provincial efforts to introduce forms of proportional representation have failed to win popular approval in referendums.

"Canadians, I submit, are open to ideas about how to modernize our electoral system but are concerned about the implications of a pure proportional system," Topps says in a policy paper released Tuesday. "A more incremental approach seems more likely to succeed."

Combined with abolition of the Senate, Topp says his parliamentary reforms would result in little additional cost.

The NDP has long advocated Senate abolition and has even refused to recognize the one New Democrat appointed to the upper chamber by former prime minister Paul Martin.

Topp says the Senate could be a serious obstacle to an NDP government.

"When we form government in 2015, it will be an immediate problem facing our government since we will be confronted with a second chamber composed of Conservative and Liberal appointees. These senators may feel free to oppose the policies on which we will have been elected."

Topp was a key backroom negotiator for the NDP during an attempt in late 2008 to form a coalition government with the Liberals, propped up by the Bloc Quebecois. Facing a confidence vote that the Conservatives were destined to lose, Prime Minister Stephen Harper asked the governor general to prorogue Parliament.

Topp is now proposing a new Parliament Act, which would prohibit a prime minister from seeking prorogation when a confidence vote is before the House of Commons.